1. Field of the Invention
The present invention relates to a laser device, and in particular, relates to a laser device which has a laser rod including alexandrite crystal and performs Q switch pulse oscillation. The present invention also relates to a photoacoustic measurement device including such a laser device.
2. Description of the Related Art
As one image inspection method which can noninvasively inspect a state inside a living body, an ultrasonography method is known. In ultrasonography, an ultrasound probe which can transmit and receive an ultrasonic wave is used. If an ultrasonic wave is transmitted from the ultrasound probe to the subject (living body), the ultrasonic wave advances through the inside of the living body, and is reflected from a tissue interface. The reflected ultrasonic wave is received by the ultrasound probe, and a distance is calculated based on the time until the reflected ultrasonic wave returns to the ultrasound probe, whereby it is possible to image a status inside the living body.
Furthermore, photoacoustic imaging which images the inside of a living body using a photoacoustic effect is known. In general, in photoacoustic imaging, the inside of the living body is irradiated with a pulse laser beam, such as a laser pulse. Inside the living body, a living body tissue absorbs the energy of the pulse laser beam, and an ultrasonic wave (photoacoustic signal) is generated due to adiabatic expansion caused by energy. The photoacoustic signal is detected by an ultrasound probe or the like, and a photoacoustic image is constituted based on a detection signal, whereby it is possible to visualize the inside of the living body based on the photoacoustic signal.
In a measurement of a photoacoustic wave, in many cases, it is necessary to emit a pulse laser beam with high intensity, and a solid-state laser device which performs Q switch pulse oscillation is used for a light source. The laser device has a laser rod (laser medium), and a flash lamp (excitation lamp) which excites the laser rod. The laser device has a Q switch for Q switch pulse oscillation. A laser device which can be used for a photoacoustic measurement is described in, for example, JP2013-089680A or JP2013-074180A. These documents describe an example where alexandrite crystal is used as a laser medium.